Compounds having a structure formed by the condensation of a nitrogen- or carbonyl-containing ring and a pyrimidine ring, for example, compounds having a pyridopyrimidine structure are known as mentioned in, for example, Chemical Abstracts, Vol. 90, 94893 (1979) and Vol. 97, 182350 (1982). However, these known compounds are greatly different in structure from the 2-piperazinopyrimidine derivatives of the present invention and their usefulness in agricultural applications are neither explained nor suggested in the above publications.
The present inventors conducted an extensive study on 2-piperazinopyrimidine derivatives. As a result, the inventors have succeeded in the synthesis of the novel 2-piperazinopyrimidine derivatives of the present invention greatly different in structure from the known compounds mentioned above and further have found that these novel compounds have an excellent herbicidal activity, and have completed the present invention.